Potatoes of the shape, size and quality normally useful for cutting into strips of the french-fry configuration are composed of, on the average, approximately 20% solid matter and 80% water. However, these potatoes typically vary in solids content from one another by as much as 5 to 6% or more. In addition, within any given potato, the solids content will vary significantly from the high moisture central core to the low moisture exterior. Thus, when potatoes are cut into strips, the strips are characterized by a wide variation in solids content depending on the particular potato and the part of the potato from which they are cut. Subsequent uniform frying of the strips from such a potato or quantity of potatoes results in products of varying texture and otherwise non-uniform results. Other non-uniform results include a condition known as "sugar ends" or "whole sugar units". This extremely undesirable condition occurs when either one end of the cut strip or the entire strip is high in sugars. Upon frying, that end or unit becomes very dark and the occurrence of even minor amounts of these units can result in the product being treated as out of grade. These units are removed by solids separation because the high sugar portion is of low specific gravity.
Tonnage production of such fried strips where uniform results are requisite is thus extremely difficult to achieve. The art has long recognized the problem and has coped with it by simply overprocessing the high solids strips (highest quality) to ensure that the low solids strips (lowest quality) are adequately blanched and fried to the minimum level of cooking in the widely varied density mixture.
Since the solids content of a potato or potato part varies directly with its density or specific gravity, a practical process for separating the potato strips by solids content is desirable. For example, a potato strip with an average solids content of 20% may have a specific gravity of about 1.080. Therefore, potato strips with a solids content of less than 20% can be removed from higher solids strips by placing the strips in a liquid medium of 1.080 specific gravity and removing all strips that float and recovering the high solids strips for french fry use having an improved and acceptable texture.
It can therefore be seen that a process for segregating raw potato strips according to solids content (density) is potentially useful for producing a more uniform quality product. Also, one main economic advantage of the process lies in the fact that more optimum processing conditions (blanching and frying) leads to reduced energy requirements, reduced oil consumption, and improved overall product yield. Improved yield means that more saleable and hence profitable finished product is obtained for the same amount of raw product processed because of the uniform nature of the process and the better quality product by a lower cost operation.
The separation of cut potato strips into categories has also been proposed heretofore. U.S. Pat. No. 2,681,285 to Hendel et al is directed to a process of segregating potato tissue wherein the cut potatoes are subjected to density fractionation in a solution to isolate denser pieces having low browning tendencies as part of a process for preserving the brine solution prepared by dissolving common salt in water to produce a solution having a specific gravity in the range from about 1.060 to about 1.090. The potato pieces which sink and the potato pieces which float are separately removed. Mention is made that other non-toxic solutions of the proper specific gravity may be used instead of the brine solution Specific mention is made of calcium chloride, potassium chloride, sucrose and dextrose. All such separating media are in the form of solutions and not suspensions and although starch was available in large quantities at low cost at the time Hendel's invention, in 1952 the advantages thereof such as low processing costs and low material costs to produce a suspension to facilitate fractional separation was not recognized.
Basically, Hendel desires to separate the tissue of high browning tendency from the tissue of low browning tendency. In any event, the process utilizes a solution, be it a brine or one of the other solutes intended to produce a fractionating medium and not a suspension as contemplated by the present invention.
Although described as non-toxic, brine solutions and many of the other materials mentioned may be hazardous to the environment. Further, the residual salt left in the treated potato products represents an undesirable product for consumers. For various reasons, this particular proposal has not been successful and is not used commercially.
U.S. Pat. No. 2,426,398 to Lathrop discloses a method and apparatus for grading whole potatoes which also utilizes a brine solution of predetermined density. According to the patent, potatoes of higher specific gravity and greater density sink in the brine solution while potatoes of lighter specific gravity float at the surface of the solution and are skimmed off and removed. The process can be repeated with solutions of varying specific gravity so that the steps are repeated as many times as necessary for the number of grades of potatoes desired to be recovered. However useful such a process may be, it is only an arrangement for grading potatoes and does not disclose the separation of the parts cut from a given potato preparatory to freezing, frying or other processing steps, and wherein such parts have variations in density or solids content.
Several types of special separating equipment that employ conveyors which move potato strips and different grades of potatoes and other products after they have been separated by classification in a sink-float type of separator have been proposed in the art. Such equipment is disclosed in Lathrop U.S. Pat No. 2,426,398 and Olney U.S. Pat. No. 2,571,056. However useful such a process may be, in each instance the arrangements of conveyors and tanks are unique to the particular separating system to which the patents are directed and not useful in other systems and hence are not able to produce the results of the present invention.
One such patent of interest is Gunnerson U.S. Pat. No. 4,169,787 to a method and apparatus for separating raisins from the stems, caps, mold and other inedible portions thereof. It employs a complicated set of hipped discharge conveyors that receive two fractions of the treated materials, one being the edible raisins and the other portion being the inedible materials, after their separation by a solution utilizing differential specific gravity. The separation of Gunnerson is relatively easy because there is a relatively large gap in specific gravity between the two dissimilar materials, namely, raisins and inedible trash. In separating low and high solids strips, it is necessary to deal with a specific gravity continuum of like materials and therefore, control of the entire process must be much more precise and the equipment must be more sophisticated in design.
Despite the fact that starch is present in many potato producing operations, there is no prior teaching of the use of starch as a solid suspension medium for separation. U.S. Pat. No. 567,790 to O'Neill discloses separating and collecting the germs from corn. A starch liquor is formed from the corn as it is ground in water and subjected to pressure and disintegrating steps. However, the starch medium is not used as a separation media and its specific gravity is not relied on because corn germ floats in plain water without the addition of a medium such as sodium chloride or starch and to a large extent the separation is effected by mechanically agitating the hulls to cause them to rise to the top of the starch liquor as the solids pass to a sieve. The starch liquor is thus not necessary for this to operate as a sink-float separation medium.